EXPRESSION OF CDX-2 IN THE MOUSE EMBRYO AND PLACENTA - POSSIBLE ROLE IN PATTERNING OF THE EXTRAEMBRYONIC MEMBRANES

Three mouse homologues of the Drosophila homeotic gene Caudal (Cad) ha ve been described. They are currently designated Cdx-1, Cdx-2, and Cdx -4, Cdx-1 and 2 are both strongly expressed in the adult mid- and hind gut, while Cdx-1 and 4 have been shown to be activated in the embryoni c primitive streak, Using a polyclonal antibody against a fusion prote in containing the amino terminal 109 amino acids of murine Cdx-2, we h ere describe the topographical location of the gene product from early cleavage to 12.5 days of embryonic development. Cdx-2 expression begi ns at 3.5 days and is confined to the trophectoderm, being absent from the inner cell mass. Subsequently, staining is located in the extra-e mbryonic ectoderm adjacent to the epiblast, but sparing the more super ficially placed polar, as well as the mural trophoblastic cells. Conti nuing expression in the fetal membranes involves the chorion, the alla ntoic bud, and, at even later stages, the spongiotrophoblast. From 8.5 days, Cdx-2 begins to be expressed in embryonic tissues, principally (unlike Cdx-1) in the posterior part of the gut from its earliest form ation, as well as in the tail bud and in the caudal part of the neural tube. Cdx-2 is, therefore, transcribed well before any other membrane of the Cad homologue group and of the related Hox-C group; its expres sion in the extra-embryonic membranes and in the hindgut reflects the phylogenetic relationship between the cloaca and the chorio-allantois and suggests the possibility that homeobox genes may be involved in pl acental development and/or patterning. (C) 1995 Wiley-Liss, Inc.